Question

The cell membranes of adjacent cells are fused at the cell junction known as
A. Macula adherens
B. Zonula occludens
C. Zonula adherens
D. Nexus

Answer 1

Hint: Tight junctions, also known as occluding junctions or zonula occludens are multiprotein junctional complexes whose function is to prevent leakage of transported solutes and water and seals the paracellular pathway. Leaky pathways are also called weak junctions that are formed by selective channels of small anions, cations, and water when required in some cases.

Complete answer: The branching network of sealing strands are present in tight junctions. The stand of these junctions acts independently towards each other. A row of transmembrane proteins is embedded in extracellular domains and cell proteins that are directly joined together. Both transmembrane and cytoplasmic proteins are present in these junctions. Occludin, claudins and junction adhesion molecule (JAM) proteins are the three major transmembrane proteins. Different peripheral membrane proteins such as ZO-1 are associated and are located on the plasma membrane of the intracellular side. The strands of the active component of proteins are anchored by this. Cytoskeletons of adjacent cells are joined together by the tight junctions that hold the cells together. It acts as a barrier, which is of two types that are performed based on the function needed in the body; protective barriers and functional barriers serving purposes such as osmotic balance maintenance and material transport. The polarity of cells is maintained by the tight junctions that prevent integral membrane proteins lateral diffusion.
Hence, the correct answer is option B.

Note: Occludin was the first integral membrane protein to be identified. It has a molecular weight of 60kDa. It consists of four transmembrane domains and both the N-terminus and the C-terminus of the protein are intracellular. It forms two extracellular loops and one intracellular loop. These loops help regulate paracellular permeability.